Stem cell 'zoo' may save rare species

Marlowe Hood, Paris

This adult white rhinoceros and her calf are two of only seven left in existence. Photo: Martin Harvey/WWF

SCIENTISTS say they have produced the first stem cells from endangered species, a breakthrough that could potentially save dozens of animals teetering on the brink of extinction.

''The best way to manage extinction is to preserve species and habitats but that is not always working,'' said Oliver Ryder, director of genetics at the San Diego Zoo and co-leader of the study. ''Stem cell technology provides some level of hope that they won't have to become extinct even though they have been completely eliminated from their habitat.''

That is the case for the northern white rhinoceros, one of the first two animals included in Ryder's new ''stem cell zoo''. Only seven specimens remain in existence, all in captivity and two in San Diego.

The researchers also isolated stem cells from a critically threatened primate called a drill, genetically a close cousin to humans. In captivity, drills often suffer from diabetes, a disease scientists are seeking to treat in humans using stem cell-based therapies.

Dr Ryder's team had collected skin cells and tissue samples from more than 800 species, stored in a ''frozen zoo'', by 2006.

That is when he contacted Jeanne Loring, a professor at the Scripps Research Institute in nearby La Jolla and the study's other lead researcher, about the possibility of using the bank to generate and store stem cells.

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At the time, scientists seeking to use stem cells to cure human disease had not yet found a reliable technique for turning normal adult cells into stem cells that can give rise to nearly any type of tissue or cell in the body.

Today, however, this process, called induced pluripotency, is routinely achieved by inserting certain genes into normal cells.

At first, Dr Ryder and Dr Loring tried to use genes from animals closely related to the target species in order to trigger the transformation, but the experiments failed. Through trial and error, they discovered to their amazement that the same genes that induce pluripotency in humans also worked for the drill and the rhino.

The process is inefficient, producing only a few stem cells at a time, according to the study, published in Nature Methods. But it was still enough to start the ''stem cell zoo''.

Perhaps the greatest potential for helping endangered species - beyond disease treatment - is new reproductive strategies. If adult stem cells can become a sperm or egg cell, for example, scientists could then use skin cells from long-dead animals in the frozen zoo to produce the male and female starter kit for new life.

Induced sperm cells could be combined with the eggs from living animals through in vitro fertilisation. Or, both eggs and sperm might be generated from stem cells, with the resulting embryos implanted in live host animals.